The present invention relates to apparatus for making a gatefold in a central portion of a sheet and, more particularly, to such apparatus which includes a gatefold pan assembly having a deflector and a sensor for controlling retraction of the deflector as the sheet begins to leave the pan.
A gatefolded sheet is one which has been folded three times so as to contain four leaves. The two outer leaves are folded inward initially along two parallel fold lines, and the resulting folded sheet is again folded along its centerline. The center fold, known as a gatefold, presents certain problems in automatic folding operations, particularly in view of the two previously folded, inwardly extending end leaves.
Because of these problems, various specially designed devices have been used to perform the gatefold operation. One such device, disclosed in U.S. Pat. No. 4,419,088, issued Dec. 6, 1983, to Nemec, utilizes a vertically movable gate assembly which includes a blade. When the blade is lowered, it drives the folded sheet down into the nip between two rolls to form the gatefold. A limit switch with a sensing arm detects the position of the sheet and activates the folding mechanism. Another specially designed gatefold device is shown in U.S. Pat. No. 3,901,501, issued Aug. 26, 1975, to Kistner. The Kistner device, like that disclosed in Nemec, includes a blade which is lowered to drive a sheet into the nip between two rolls to form the gatefold. The Kistner device further includes guiding tongues to either side of the blade which move downward with the blade and insure that the ends of the outer leaves also are pressed into the nip between the two rolls.
Such specially designed, stand alone equipment for performing a gatefold operation has the disadvantage that it is relatively inflexible in use and, in some instances, may not be conveniently mated to the folding equipment which performs the balance of the folding operations. One approach to dealing with these problems has been to perform the gatefold operation in a conventional buckle folding machine. A buckle folding machine includes a series of rolls and fold pans. A sheet of paper to be folded is inserted between two rotating rolls of a first roll set and is driven by these two rolls into a fold pan of a fold pan assembly. A forward edge of the sheet eventually strikes a paper stop in the fold pan; however, the two rolls continue to feed the sheet forward. Thus, the sheet buckles and the bulge of this buckle eventually extends between two rolls of a second roll set. These rolls fold the sheet at the bulge and feed this folded edge into a second fold pan assembly. Upon striking a second paper stop there is a new buckle in the sheet and this buckle is, in turn, inserted between two rolls of a third roll set. This process continues until the sheet is folded a desired number of times.
When it is desired to perform a gatefold operation, a special gatefold pan assembly is substituted for one of the fold pan assemblies of the buckle folding machine. The gatefold pan assembly includes a movable deflector which is moved into position adjacent the roll set associated with the gatefold pan assembly at the proper time to insure that the ends of the outer leaves are also inserted into the nip between these rolls along with the bulge in the central portion of the sheet at the gatefold line.
In the past, the timing for actuation and deactuation of the deflector has been determined by a sensor positioned on the fold pan which precedes the gatefold pan assembly in the sheet path through the folding machine. Actuation occurred as the sheet left the fold pan and deactuation was effected a fixed time thereafter. Problems have occurred with this arrangement when the speed of operation of the machine has fluctuated. Additionally, the fixed time for deactuation varies as sheet sizes are changed, thus requiring that the operator of the folding machine adjust this time period at the beginning of each folding job. This has been time consuming since it has typically been accomplished empirically. It is seen, therefore, that a need exists for apparatus for performing a gatefold operation which is not subject to these problems.